1. Field of the Invention
The invention relates to a method and a system for appraising the wear of axles of a robot arm of an industrial robot.
Methods for appraising the wear of axles on industrial robots that are based on the mechanical measurement of the axial backlash and appraise axial wear on the basis of the values measured are generally known. The appraisal is generally performed by the operating or service personnel, who can, on the basis of values obtained in their experience with handling the robots, interpret the measured values in such a way that on the one hand the state of wear is established, on the other hand a statement can be made as to whether and which measures have to be performed on the axles of the robot.
2. Summary of the Invention
It is accordingly an object of the invention to provide a method and a system for appraising the wear of axles of a robot arm which overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, with which wear can be determined in the simplest possible way.
Accordingly, the method according to the invention for determining the wear of axles of a robot arm of an industrial robot has the following method steps. A torque profile of at least one axles during at least one working cycle of the industrial robot is taken as a basis for an analysis. The torque profile is analyzed for portions of the torque profile that leave a previously fixed torque band, and current axial wear is determined by assessing the frequency and/or the curve profile of the portions of the torque profile.
One advantage of the method according to the invention is that only a torque profile of the axle to be considered of the industrial robot is required in order to appraise axial wear. It is of secondary importance here whether the torque profile is measured at the time or is read out from an earlier measurement that has been stored in a data memory.
The proposed method considers in particular a working cycle or number of working cycles of the industrial robot. In principle, any time segment during the movement sequence of the industrial robot may be chosen as the working cycle. It is particularly meaningful, however, for a movement sequence of the industrial robot which the latter keeps repeating to be chosen as the working cycle, so that all the movements, all the tasks and all the loads that are performed during a repeat cycle, from the beginning of the performance of a task to the end of the performance of the task, are included. Such a working cycle therefore covers all the tasks and loads of the industrial robot. The wear appraisal for the axles concerned of a robot arm is accordingly accurate.
The analysis of the torque profile for portions of the torque profile that leave a previously fixed torque band and the assessment of the frequency and/or the curve profile of the portions of the torque profile take place according to the invention in an automated manner. This dispenses entirely with the previously necessary interpretation by operating or service employees specializing in this. In this way, the amount of data considered for the torque profile can be increased and the accuracy of the wear determination is enhanced. Altogether, the method according to the invention is consequently quicker and more accurate than those previously known.
An advantageous development of the method according to the invention is characterized in that the ratio of a maximum torque value to an averaged torque value in a previously defined time period within the working cycle considered is used for the assessment of the axial wear.
In the analysis of the torque profile, individual portions of the torque profile having a maximum torque are analyzed in particular, the rotational direction of the torque being immaterial. The portions of the torque profile are analyzed as to whether they have a maximum that goes beyond a previously set torque band, with the result that a torque loading exceeding the torque band has occurred. These maximum or extreme torque values are one of the factors responsible for increased wear of the axles and are accordingly taken into account in the assessment. The ratio mentioned at the beginning of maximum torque values to averaged values can be adapted more closely to a weighting factor, which is empirically determined.
A further form of the method according to the invention is characterized in that at least one curve profile, in particular the slope of the curve at a time directly before and possibly after an extreme, taken from the latter up to at least the next-following point of inflection of the torque curve, of a portion of the torque profile is used for the assessment of the axial wear.
For the assessment, therefore the steeply rising or steeply falling torque profiles in particular lead to a different basis for the assessment of the axial wear than for example shallow curve profiles. This has to be taken into account for example by different assessment factors, which are included in the assessment formula.
The set object is also achieved by a system for determining the wear of axles of a robot arm of an industrial robot, with a data module, which contains the data of a torque profile of at least one axle during at least one working cycle of the industrial robot, with an analysis module, with which portions of the torque profile that leave a previously fixed torque band can be selected, and with an assessment module, by which the frequency and/or the curve profile of the portions of the torque profile can be interpreted as axial wear, a data exchange between the data module, the analysis module and the assessment module being made possible.
The system for determining the wear of axles of a robot arm has three different functional modules. The functional module referred to as the data module contains the data of the torque profile to be considered or of the torque profiles to be considered in the event that a number of axles are being considered. In the analysis module, specific data provided by the data module can be selected in the way specified. In particular, those portions of the torque profile that leave a previously fixed torque band, that is to say have comparatively high torque values, are to be used for the instances of axial wear that are then to be appraised in the assessment module. In this case, the torque band is generally defined such that the limits of the band correspond to the permissible axial loading of the respective axle, for example coinciding with the limit-value loading specifications of a robot manufacturer or adopted with other empirically established limit values.
In an advantageous basic variant, the system according to the invention for determining wear requires no additional measured value pickups or other measuring devices that would not already be on the robot. Consequently, the construction is comparatively simple and the wear appraisal can be carried out particularly quickly and comparatively accurately on account of the automation of the system concerning the handling of the data, the analysis and the assessment of the data. In the basic variant as described above, the required data are taken from a robot control.
A development of the system according to the invention is characterized in that at least one of the modules is disposed in a robot control.
This additionally simplifies the equipment required. This is so because the robot control is a customary part of a robot system, so that the implementation of the module or modules in the robot control results in a particularly compact system.
However, it is also quite possible for individual modules or all the modules to be integrated in an evaluation device, in particular a measuring computer.
This achieves the advantage that the system according to the invention becomes mobile and is suitable for successive use on a number of industrial robots.
Furthermore, it is immaterial for the system according to the invention whether the torque profile can be read out from the robot control as direct or indirect values.
When indirect values of the torque profile are read out from the robot control, the torque values that are current at the time or else any stored torque values can be called up as the torque values. The system according to the invention can in this case detect a torque value or torque values without further data preparation. Indirect values refer to those values that are either available as an unscaled voltage value of the robot control or are made available as an analog voltage signal or other signal and first have to be interpreted or converted as a torque value. For this purpose, an analog-digital converter or some other transfer module may be disposed upstream of the system according to the invention.
In an advantageous form of the system according to the invention, the modules are in each case configured as computer program products.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and a system for appraising the wear of axles of a robot arm, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.